The advanced spacecraft, also known as TDRSS for the whole system or
TDRS for an individual spacecraft, and its greater capacity is needed to
keep the communications network on pace as NASA's fleet of research
satellites has increased.

"It has some higher bandwidth speeds," said Diana Calero, mission
manager for NASA's Launch Services Program, or LSP, based at Kennedy
Space Center in Florida. "We have some aging satellites, so we need some
new spacecraft to go in there and carry some more of the bandwidth."

It will take about half an hour for the spacecraft to unfold its two
circular antennas and a pair of large solar arrays as it climbs to its
destination. Onboard thrusters will provide the final guidance for the
spacecraft as it settles into its operational location.

"The antennas are furled and they have a margin, a certain amount of
days that they can stay furled," Calero said. "If they pass that margin,
then the antennas, when they're deployed, they can actually have a
degradation in space and so we have to play close attention to how long
that stays furled. So it was really challenging trying to schedule the
shipping of the spacecraft with the launch date. We're still watching it
very closely."

TDRS-K is the 11th TDRS launched by NASA since it began building
the space-borne network in 1983. The most recent spacecraft launched in
2002.

"We haven't launched a TDRS in about 10 years so it's really good to have this," Calero said.

The new TDRS will be able to transmit several times more information than its predecessors.

"In terms of bandwidth capability, it's probably four or five times
higher bandwidth improvement" said Paul Buchanan, deputy project
manager for TDRS.

Orbiting about 22,300 miles above Earth, positioned roughly over Hawaii,
TDRS-K will put a myriad of antennas to work to receive and transmit
signals from a wide range of spacecraft to Earth and vice-versa.

Even rockets carrying NASA spacecraft carry TDRS-compatible
communications gear and transmit telemetry through the orbiting network
instead of ground stations, an advancement that saves NASA money by not
having to field specialized aircraft and ships or open a string of
remote stations to monitor a launch.

The number of satellites required to serve NASA's orbiting fleet of
scientific spacecraft has grown to such an extent that the TDRS network
already operating in orbit plus the TDRS-K and two identical TDRS
spacecraft launching next year and in 2015 will have plenty of commands,
telemetry and data to relay.

"All the Hubble pictures come through TDRS, all the video that we see
from the space station and the astronauts and the video we saw from the
shuttle, it all comes through TDRS, and then we have all the
Earth-orbiting satellites, all that data comes through TDRS," Buchanan
said.

The communications constellation replaced the ground stations positioned
on Earth so NASA could communicate with astronauts in orbit. That
system allowed contact only when the spacecraft passed within range of
the antennas, however. With TDRS satellites in place, controllers have
near-constant contact with spacecraft.

"If you roll back in history maybe 30, 40 years, back in Mercury days
and Apollo there were no TDRS satellites for communication so you had
outages between the ground stations," Buchanan said. "We didn't want the
outages, we wanted continuous (communications), so that's what prompted
the TDRS."

Six TDRS spacecraft are operational in orbit, one new satellite is in
orbital storage ready to take the place of an older TDRS and two older
models have been retired. The oldest one still working is TDRS-3,
launched in September 1988 aboard the space shuttle Discovery.

"We've had to decommission two legacy spacecraft in the last year or two
due to the fact that electronics start to die after 20, 25 years,"
Buchanan said. "We're launching now for an immediate need and
replenishment schedule. I think it's a fine balance between the existing
system and replenishment."

When their service life is up, the TDRS satellites are moved farther
from Earth into what's called a storage orbit about 250 miles higher.